U.S. Pat. No. 3,653,089 discloses an aerated bed pad having interlaced chambers which are alternately inflated from a pressure source and which are cyclically deflated by reason of the escape of air through perforations in the top surface of the pad. The escaping air passes into a foam sheet which overlies the pad, such sheet not only diffusing the escaping air but also serving as a means for absorbing perspiration and drawing it away from the patient, thus preventing or greatly reducing maceration of tissue. The air discharged from the pad into the foam sheet assists in the evaporation of moisture from that sheet. A system embodying such features, intended primarily for reducing the development of decubitus ulcers in bedridden patients, has been commercially available for a number of years through applicant's assignee, such system being marketed as the Lapidus Air Float system.
The commercial Air Float system has utilized a rotary compressor for delivering a smooth non-pulsating stream of pressurized air alternately to each of the inflatable chambers of the pad. While pulsatile pumps or compressors of the piston or diaphragm type are well known for a variety of other applications, their use with inflatable pads has not been considered advantageous, at least to the extent that pulse-dampening chambers are thought to be necessary for the purpose of smoothing out the pulses developed by such pumps. See, for example, U.S. Pat. No. 3,462,778 which discloses a need for a pulse dampener interposed between a pulsatile pump and an inflatable-deflatable pressure pad. Other patents of general interest are U.S. Pat. No. 3,148,391, 3,672,354, 3,866,606, 3,297,023 and 3,008,465.
One aspect of this invention lies in the discovery that a pulsatile air pump or compressor is not undesirable but is in fact highly advantageous in an alternating pressure pad system if that system is of the particular type disclosed in U.S. Pat. No. 3,653,083; that is, a system in which air is discharged upwardly from perforations in the top of the pad and into a resilient sheet of foam or other porous moisture-absorbent air-permeable material. Specifically, it has been found that the pulsatile discharge of air through the tiny openings of the pad tends to promote the rapid evaporation of moisture absorbed by the cover sheet. Since the sheet is interposed between the patient and the pad, and since the sheet serves as a dampener as well as a diffuser, no streams of pulsating air impinge directly on the patient. Any pulsations or changes in pad pressure tend to be sensed as pleasant vibrations having a mild stimulating or circulation-promoting effect.
In brief, the system includes a pad having two sets of interlaced inflatable-deflatable air chambers or passages and having a multiplicity of perforations through its top surface to permit the controlled escape of air from those chambers where they are inflated. A porous air-permeable liquid-absorbing sheet covers the top surface of the pad and serves to absorb perspiration from a patient as well as to diffuse air discharged through the pad's perforated top surface. As already indicated, a distinctive feature of the combination lies in the fact that the inflating means for cyclically and alternately inflating each of the chambers of the pad while the other of such chambers is deflating takes the form of a pulsatile pump or compressor which is capable of pulsing the air supplied to the pad at a frequency within the general range of 15 to 65 pulses per second, the preferred range being about 25 to 35 pulses per second. Because of the rapidly pulsing discharge of air through the perforations of the pad and into the fluid-absorbing cover sheet, liquid held by the cover sheet tends to be dispersed and the evaporation of such liquid is thereby promoted.
The assembly also includes a control valve for redirecting the air from the pulsatile pump along an alternate route containing a flow restrictor which dampens out the pulses in the pressurized air flowing to the pad. Therefore, through selective operation of the control valve, a user may or may not avail himself of the benefits of pulsating discharge of air into the porous moisture-absorbent cover sheet.
Slight undulations occur, alternating pressure points and stimulating peripheral circulation, as the chambers of the pad are alternately and cyclically inflated and deflated. Solenoid-operated valves and solid-state electronics are used to control the flow of air to the respective chambers and, because of the sharp cut-off and onset of air flow which such valves produce, the system of the present invention is ideally programmed so that the inflation of each chamber commences just slightly before the flow of air to the other chamber is discontinued. The extent of overlap falls within the general range of about 0.3 to 3.0 seconds and insures that no objectionable rise-fall effects, and no momentary bottoming out effect, will occur during pad operation.
Other features, advantages, and objects of the invention will become apparent from the drawings and specification.